Selectively bleaching dyes and pigments in developed electrophotographic layers

ABSTRACT

Toning an electrophotographic layer by adding materials which bleach at different rates and thereafter selectively bleaching the materials after development.

United States Patent [191 Takimoto et al.

[ SELECTIVELY BLEACHING DYES AND PIGMENTS 1N DEVELOPED ELECTROPHOTOGRAPHIC LAYERS [75] Inventors: Masaaki Takimoto; Satoru Honjo,

both of Asaka, Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: -Sept. 6, 1973 [21] Appl. No.: 394,808

Related US. Application Data [63] Continuation-impart of Ser. No. 197,493, NOV. 10,

[52] US; Cl 96/1 R, 96/1.6, 96/1.7, 96/53, 8/111 [51] Int. Cl G03g 13/22 [58] Field of Search 96/1 R, 1.6, 117, 53;

[56] References Cited UNITED STATES PATENTS 2,005,448 6/1935 Aisen 8/111 X 1 Feb. 18, 1975 Gaspar 96/53 Eastman 96/1 R Bresina et al. 96/1 R Menold et a1 96/1 R Fox et a1 1 96/1.6 Rees 96/1 R Gilman et al. 96/l.6 Manhardt 96/1.7 X Contois 96/1.5

Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or Firm-J. T. Martin; Gerald J. Ferguson, Jr.; Joseph J. Baker ABSTRACT 21 Claims, N0 Drawings CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U.S. patent application Ser. No. 197,493 filed Nov. 10, 1971.

BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates to a process for toning a colored electrophotographic photosensitive layer after a developing treatment.

2. Description Of The Prior Art It is known that an electrophotographic photosensitive layer cna be .produced by dispersing a photoconductive powdered material into a resinous binder, and for this purpose, various photoconductive materials are already known to be usable such as cadmium sulfide, zinc oxide, zinc sulfide, etc. Though the color of the electrophotographic photosensitive layer is not an important factor in electrophotographic processes containing the step of transferring a toner image onto an ordinary paper sheet, the color significantly affects the final image quality obtained if the process does not contain such transfer step. In the case of using such a photoconductive powdered material, however, spectral sensitizing dyes are frequently added in order to correct the spectral sensitivity thereof.

Consequently, it has been necessary to prepare a photosensitive layer making a compromise between the Such spectral sensitizing dyes show fading at different rates when an electrophotographic photosensitive layer containing the same is exposed to light. Consequently, if the color ofa photosensitive layer is selected to compromise with spectral sensitivity directly after developing, discoloration or fading of the photosensitive layer after a period oftime may result in a disagreeable color. However, in the case of storing an unused electrophotographic photosensitive layer in a dark place, it is possible to obtain a fairly long shelf life even when such elements are sensitized with cyanine dyes which generally show very poor stability against light. This long shelf life often leads to a careless selection of sensitizing dyes without giving consideration to the light fastness thereof, and it is often impossible to maintain final image quality at a constant level for a prolonged period. In order to prevent this drawback, it has been proposed to remove the sensitizing dye from the electrophotographic photosensitive layer after the depigment used as the toner and the resin component em- 7 ployed in the developer.

SUMMARY OF THE INVENTION The present invention provides a process for toning electrophotographic photosensitive layers which comprise a photoconductive powdered material and a resinous binder which comprises adding a specific dye or specific dye and pigment thereto and selectively bleaching said dye or said dye and pigment after the developing treatment. Any liquid developer containing toner which does not discolor in the processing solution on toning aftertreatment is operable such as disclosed in U.S. Pat. Nos. 2,907,674; 3,081,263; 3,058,914; 3,198,649; 3,259,581; 3,337,340.

DETAILED DESCRIPTION OF THE INVENTION There is no limitation on the photoconductive powdered material used in this invention and common materials such as zinc oxide, zinc sulfide, cadmium sulfide, titanium dioxide, indium trioxide, anthracene, etc., are easily used.

Further, any resinous binder which does not affect the photoconductive powder may be used such as'silicone resins, alkyd resins, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, polystyrene, polyalkyl methacrylate, polyalkylacrylate, styrene-butadiene copolymer epoxy resins, epoxy ester resins, etc.

Selective bleaching of a coloring material contained in an electrophotographic photosensitive layer after developing, which is an essential step of the process according to this invention, can be conveniently carried out by exposure to strong light irradiation, particularly ultraviolet irradiation, by an acidic or alkaline bleaching bath or by chemical treatment with substances containing peroxides. The bleaching step may simultaneously perform other functions such as washing, drying, fixing the electrophotographic photosensitive layer to hold a reproduced image thereon, or forming a surface protective layer on the layer in addition to the bleaching operation.

It has already been proposed to apply a transparent lacquer on the surface of an electrophotographic photosensitive layer holding a reproduced image thereon in order to fix the image and simultaneously form a surface protective layer, and the objects of the present invention can be simply realized by adding a small amount ofperoxide to such a transparent lacquer. In this case, it is naturally necessary to add coloring materials capable of being easily bleached by such a peroxide in the lacquer and coloring materials relatively stable against the peroxide in a suitable ratio into said electrophotographic photosensitive layer at the preparation thereof.

Fixing and surface protection of an image can also be achieved by laminating a transparent film onto the surface of an electrophotographic photosensitive layer after developing, and a similar effect to that described above is obtained if a peroxide is added to the adhesive material employed for the lamination.

U.S. Pat. No. 3,250,614 discloses decoloring the sensitizing dye in a photoconductive layer using an organic acid.

On the other hand, this invention relates to toning method of decolorizing the easily decolorized dye using peroxide, utilizing the difference of the decoloration degree of the sensitizing dyes, followed by decoloration with light, if desired. Accordingly, it is necessary to select the sensitizing dyes for effecting the above purpose.

Electrophotographic photosensitive layers generally employed in the reproduction area are adjusted to a neutral color by means of sensitizing dyes or by toning agents and is generally preferred to illustrate, after developing, a bluish or greenish color rather than a yellowish or pinkish color. Consequently, it is desirable to incorporate into the photosensitive layer a yellow or pink coloring material with relatively low stability against light or chemicals and blue or green coloring materials with a relatively high stability. In spite of such a general tendency, however, it is possible to bleach any color selectively by the correct choice of coloring materials of suitable stability to be added in the electrophotographic photosensitive layer, for example, in order to meet personal taste or to classify images by the color of the subject or the background.

Any electrophotographic photosensitive layer containing a coloring material may be employed in the present invention. It is desirable, however. to clarify the purpose of addition of each coloring material. For in stance. cyanine or merocyanine dyes can be subjected to toning according to the present invention because of their relatively low light fastness or relatively low stability against peroxides (in comparison with xanthene or azo dyes). ln greater detail, an electrophotographic photosensitive layer can be prepared in a neutral color by regulating the amounts of fluorescein and rose bengal (xanthene dyes) and brilliant blue FCF (triphenylmenthane dye). Such a photosensitive layer can have further added thereto a cyanine dye in order to improve the spectral sensitivity, and a transparent lacquer containing a peroxide can be applied after developing to fix the reproduced image and to protect the surface of the layer. Successive exposure to light causes selective bleaching of the cyanine dye to provide a reproduction with a background of nearly neutral color which provides increased brightness after prolonged exposure to light.

For certain purposes, a photosensitive layer is provided with almost equal sensitivity to blue, green and red light. In such a case, it is necessary to increase the sensitivity of the layer to the blue and green wavelength regions when a tungsten lamp is to be used as the exposure light source. and such modification inevitably results in a reddish color in the layer. This red coloration can be compensated for by adding a dye and/or pigment which is capable of absorbing red light but incapable of spectral sensitization in the electrophoto graphic process, but such addition not only significantly lowers the brightness of the photosensitive layer, but also the efficiency of the sensitizing dye in the red wavelength region. According to the present invention, on the other hand, the above drawback is removed by employing sensitizing dyes of distinctly different fading rates for the red region and the blue-green regions and also by employing dyes for the latter-regions in relatively large amounts. More specifically, the purposes of this invention can be realized by using cyanine or merocyanine dyes for sensitization in the blue and green regions and relatively phthalocyanine dyes for the red re gion accompanied by selective fading by, tag, applying an acrylic lacquer containing a peroxide for surface protection. Cyanine and merocyanine are stable provided they are stored in the dark because they are relatively quickly decolored when exposed to light and given a decoloring treatment. When they are used, they give a desired spectral density.

The coloring materials which are preferably used in the present invention are classified according to the following three groups (a), (b), and (c):

Group (a) includes coloring materials which have high fading rates that is, low light resistance, group (b) includes coloring materials which have low fading rates that is, high light resistance, and group (c) includes coloring materials which have medium fading rates that is, medium light resistances falling between those of groups (a) and (b).

Representative coloring materials of group (a) are cyanine dyes such as 3,3'-di-B-carboxyethyl-thiacarbocyanine-bromide, merocyanine dyes such as 3- carboxymethyl-5-[(3-ethoxycarbonylmethyl2(3H)- thiazolinilidene)ethylidenelrhodanine; representative coloring materials of group (b) are azo dyes such as Acid Red 27, anthraquinone dyes such as Acid Green 25, phthalocyanine dyes such as Direct Blue 86, inorganic pigments such as cadmium sulfide, organic pigments such as phthalocyanine pigments (e.g., Pigment Blue 15), quinacridone pigments (e.g. Pigment Violet l9), azo pigments (cg. Pigment Red 57, Pigment Yellow 12); and representative coloring materials ofgroup (c) are triphenylmethane dyes such as Acid Blue 9, xanthene dyes such as Acid Red 87, sulfonephthalein dyes such as dibromo-dichloro-phenol sulfonephthalein, etc. I

The differences of the light resistance between the coloring materials in the respective groups are particularly effective in the presence of peroxides.

In order to efficiently attain the purpose of the present invention, it is preferable that the coloring materials of group (e) have the main spectral sensitizing effect and the coloring materials of the other groups (a) and (b) complement this effect.

When the background color is adjusted by the action ofa coloring material of group (c) and the spectral sensitivity is complemented by that ofgroup (a), the coloring material of group (a) will be rapidly bleached in the toning process after the developing treatment and the electrophotographic material will have the finally desired color. See Example 1, Sample D, hereinafter, for an example of a combination of groups (a) and (c).

When the background color is adjusted by the action ofa coloring material of group (c) and the spectral sensitivity is complemented by that ofgroup (b), it is possible to impart a spectral sensitizing effect and, in addi tion, the background color may be changed to the specific and desired color at the same time. That is, if a coloring material of group (c) is bleached in the toning process after the developing treatment, desired coloring of the'background can be achieved since the coloring material ofgroup (b) remains. See Example 2, Sample E, hereinafter, for an example of a combination of groups (b) and (c).

Of course, it is possible to use the coloring materials of groups (a), (b) and (c) together to adjust the coloring. Examples of this are given in Example 3, Samples F, G, and H.

The coloring materials of the above-mentioned groups (a), (b) and (c) are classified according to the respective absorption rate variations thereof.

An electrophotographic photosensitive material having an electrophotosensitive layer which consists of parts by weight of zinc oxide, 12 parts by weight of styrenated alkyd resin (Japan Reichhold; Styresol No. 4400), 8 parts by weight ofpolyisocyanate (Bayer; De-

prepared, and the variation amount of the spectral abtaining a peroxide in the adhesive material therefor has marked advantages as explained above enabling fixing and protection of the image to be obtained at the same time.

sorption by a light irradiation was measured in each A examplg f h a transparent 1aquer 15, f case to examine the absorption rate variations thereof. ample, as f ll TABLE Structure of Example of Absorption Group Coloring Coloring Rate* [(a), (b) or Material Material Variation (c cyanine dyes 3,3-di-fi carboxyethyl-thiacarbocyaninc-bromide 30 (a) rnerocyanine dye 3-carboxymethyl- 5-[(3-ethoxycarbonylmethyl-Z (3H)-thiazoli nilidene)ethylidene]- rhodanine 18 -(a) phthalocyanine pigment Pigment Blue 0 (b) quinacridone pigment Pigment Violet l9 0 (b) azo pigment Pigment Red 57 l (b) azo pigment Pigment Yellow l2 0 (b) inorganic pigment cadmium sulfide 0 (b) azo dye Acid Red 27 2 (b) anthraquiiione dye Acid Green 2 (b) phthalocyanine dye Direct Blue 86 l (b) triphenylmethane dye Acid Blue 9 l0 (c) xanthene dye Acid Red 87 9 (c) sulfonephthalein dye dibromo-dichlorophenol-sulfonephthalein '10 (c) *Absorption rate variation (Initial absorption rate (Absorption rate after being exposed equivalent to about 100,000 lux for 2 hours) (Initial absorption rate) **The groups are classified as follows: (a): Absorption rate variation, more than l5% (b): Absorption rate variation, less than 3% (c): Absorption rate variation, 3 15% From the above results, it was confirmed that the groups of coloring materials may be effectively classitied in the present invention, according to the respec tive absorption rate variations thereof as mentioned above. The above-illustrated dyes and pigments are ones which are classified according to the structures thereof. Coloring materials which have similar structures show almost the same absorption rate variation, and these are classified in the-respective groups (a), (b), and (c) of the coloring materials in the present invention.

A further problem encountered with photocondu'ctive elements is that the resinous binder in the electrophotographic photosensitive layer may turn yellow due to photocatalytic activity of zinc oxide, etc., employed as the photoconductive material. Such a drawback should naturally be suppressed by improving the resin itself, but, according to this invention, it is possible to maintain the background at a constant neutral color by previously adding a phthalocyanine dye to said photosensitive layer in combination with other coloring materials. Although the bleaching step' according to this invention can be accomplished by various methods as mentioned above, theuse of a transparent lacquer containing 21 peroxide or a transparent laminate film con- 40 parts by weight 40 parts by weight l5 parts by weight 5 parts by weight Since a styrene-butyl methacrylate copolymer usually contains benzoyl peroxide in an amount of about 0.1% as a polymerization initiator, the transparent lacquer thus obtained will usually contain residual peroxide in an amount of about 0.01%. It is desirable to positively add benzoyl peroxide to said transparent lacquer since peroxides play an important role in the process of this invention. In case of using an acrylic resin obtained by employing azobisisobutyronitrile as a polymerization initiator, similar results can be reached by adding small amounts of benzoyl peroxide or other organic peroxides to the transparent lacquer. Benzoyl peroxide functions as a polymerization initiator for acrylic resins and possesses a strong destruction power toward the pigment.

Azobisisobutyronitrile functions as a polymerization initiator for acrylic resin and has a strong destructive power which is not as strong as benzoyl peroxide. It is well known that this compound is decomposed by ultraviolet ray irradiation and liberates peroxide.

As transparent lacquers, those that are colorless and extremely pale are preferred, and any clear lacquer commonly used for coating is operable. Clear lacquer comprising nitrocellulose, resin, and solvent is an example of such. Acrylic resins are often used. Toning agent of the pigment used as a toner may melt away depending upon the solvent used. The lacquer of the present invention preferably includes a peroxide.

The adhesive material used for laminating transparent film can be composed, for example, of material as are disclosed in US. Pat. No. 3,381,596:

butylacrylamide parts by weight Low molecular weight epoxy resin (bisphenol-A-epichlorohydrine) condensate ERL 2774 (manufactured by Union Carbide Corp.) has a my. ofabout 400, Epikota 828 (manufactured by Shell Oil Co.) has a m.w. of about 370 and may also be used.

Citric acid Peroxide 9.9 parts by weight 0.l parts by weight 0.08 parts by weight As the adhesive, colorless or pale adhesives which do not damage the toner image may be operable, such as polyvinyl acetate, polyethylacrylate, vinyl acetateethylacrylate copolymer, vinylacetate-ethylene copolymer, polyethylhexylmethacrylate, aliphatic polyester, xylene-formaldehyde resin. natural rubber, resin, hydrogenated resin, etc.

US. Pat. No. 338L596 also discloses examples of peroxides employable in this formulation and particularly suitable peroxides are hydroperoxide, hydrogen peroxide, tert-butyl hydroperoxide. cumene hydropcroxide, 2,5-dimethylhexyl-2,5dihydroperoxide, pmethane hydroperoxide, etc.

The adhesive material for laminating such a film can be of the semi-liquid type at room temperature or of the heat-sensitive type which is solid at room temperature. An efficient laminating method consists of laminating a plastic film provided with an adhesive material layer which is solid at room temperature but which is soluble in a non-polar liquid or the like employed in the liquid developing process. The film can be applied when the photosensitive layer is still wet with the nonpolar liquid after developing with a liquid developer. The objects ofthis invention can be realized, of course, by adding a small amount of organic peroxide to said adhesive material layer.

The material comprising the reproduced image is, of course, required to be stable against the reagent (for example, an organic peroxide, etc.) which is used to decompose the sensitizing dyes. Most organic and inorganic pigments, including carbon black, remain intact in the presence of a small amount of such peroxides and can therefore be satisfactorily employed in the process of this invention. Pigments excessively susceptible to decomposition, e.g., oxidation, will be easily determined by one skilled in the art.

The amount of organic peroxide in the adhesive layer provided on the plastic film or in the transparent lacquer can be within the range of 00001 0.1 gr/m of the photosensitive layer, more preferably 0.0001 0.01 gr/m An excessive amount does not lead to any addi' tional advantage. The peroxide is believed to perform a catalytic action and is frequently capable of decomposing dyes in excess of its chemically equivalent amount.

This invention will now be further clarified by the following examples:

EXAMPLE l 100 parts by weight of zinc oxide, 12 parts by weight of styrenated alkyd resin (Japan Reichhold; Styresol No. 4400 8 parts by weight of polyisocyanate (Bayer; Desmodur L; 50% xylylene solution, acid value of below 8) as the hardener and parts by weight of nbutyl acetate were mixed and blended in a porcelain ball mill for 15 hours to obtain a white suspension. The white suspension thus prepared was subjected to a sensitizing treatment consisting of the addition of one of the following three dye solutions followed by mixing a homogenizer. The product was then coated to obtain a dried coating thickness of 10 microns on a support material consisting of art paper previously subjected to surface treatment with colloidal alumina (Nissan Chemical: Alumina Sol No. After drying. the coated paper was placed in a thermostatic box at 50C for 12 hours to harden the resinous binder:

Sample A White suspension without dye addition. Sample B Suspension had added 4 mg. offluorescein, 4 mg. of rose bengal, 2 mg. of bromochlorophenol blue and 3 mg. of 3,3-di-B-carboxyethylthiadicarbocyanine bfO mide dissolved in 10 ml. of methanol (per 100 gr. of zinc oxide).

Sample C Suspension had added 3 mg. of fluorescein, 3 mg. of rose bengal and 4 mg. of brilliant blue FCF (CI. 42090) dissolved in 10 ml. of methanol (per l00 gr. of zinc oxide).

Sample D Suspension had added the solution in Sample C further containing 2 mg. of 3,3-di-,B-carboxyethylthiadicarbocyanine bromide.

The relative photosensitive of the above samples under a tungsten lamp (about 3000K) were:

The photosensitive layers prepared with the abovementioned samples provided excellent images upon exposure and development with liquid developer containing carbon black toner. Successive fixing and protection with a transparent acrylic lacquer caused a color change in the background area as shown by the C.l.E. color coordinates in Table l. The acrylic lacqucr'employed was a styrene-butyl mcthacrylate copolymer (50 :50) and contained about 0.01% of remaining benzoyl peroxide (with respect to the resin) which was added as the polymerization initiator.

' thereto the following dye solution (per 100 gr. of zinc Table 1 Sample ('ourdinzlle (LUZ (l) Clli. (2) ClE. (3) CLE (4) coordinate coordinate 4 coordinate coordinate of fresh directly after lightafter lightphotosensitive after exposure for 2h. exposure for 2 layer application without lacquer hours after of lacquer coating coating A X 0309) 0.3]09 0.3099 0.3115 y 0.3I75 0.3lX7 0.3l73 0.3205 l3 x 0.3057 0.3l0) 0.3075 0.3 l 28 y (L3 I04 0.303) 0.3l lli 0.315) X 0.30Xl 0.3074 0.3080 0.3090 y 0.3l57 0.3M} 0.31115 0.3185 I) X 03032 0.3029 0.3040 0.309] y 0.3123 0.3l42 0.3137 0.3lhl

The fading or bleaching accelerated by the lacquer coating is clearly indicated by the difference between (2) and (4) larger than the differences between (l) and (3) in Table 1. Sample B was found to be closest directly after lacquer coating (condition (2)) to the color of standard C light source, as determined by the C.l.E., which is represented by .r 0.3 l00-and y =0.3160. On the other hand, residual color, which was observed in Sample C and Sample D, was designed to come closest to the color of standard C light source a certain period after lacquer coating (condition (4)). The color of Sample B was. found to be distinctly reddish compared with the C light source at condition (4), principally because of rapid decomposition of the 3,3-di-B- carboxyethylthiadicarbocyanine bromide.

The advantages of this invention are most clearly found in the Sample D, which was designed to show high sensitivity and a residual color very close to that of standard C light source. In this example, in order to improve photosensitivity while retaining satisfactory residual color of Sample C, 3,3'-di-B-carboxyethylthiadicarbocyanine bromide was added to the photosensitive layer and decomposed rapidly after development by means of an acrylic lacquer containing a peroxide.

EXAMPLE 2 The white suspension shown in Example 1 had added oxide) sufficiently mixed and coated onto an art paper sheet previously subjected to an electroconductive treatment so as to obtain a dried coating thickness of 10 microns.

Sample E Fluorescein Rose bcngal Cl. direct blue 86 (CJ. 748l0) Methanol I (Formula I) C.I. direct blue 86 (C.I. 74180) The photosensitive layer thus prepared showed spectral absorptions at 510, 580 and 680 muand a photosensitivity about 15 times higher than that of Sample A in Example 1.

Exposure to light for 2'hours after lacquer coating as in Example 1 significantly reduced the spectral absorption at 510 and 580 m,u, while the absorption at 680 mp. remained almost unchanged to provide a somewhat bluish photosensitive layer. This change is attributable to the higher stability of direct blue 86 against peroxides as compared to fluorescein and rose bengal.

After light exposure for 5 hours, the only observable spectral absorption was that of the direct blue 86. and the photosensitive layer changed to pale blue.

EXAMPLE 3 together with one of the following coloring materials.

and blended for 16 hours in a porcelain ball mill to obtain suspensions colored pale yellow. pink and blue, respectively.

Cadmium sulfide I 0003 parts by weight Sample F Sample G Brilliant Carmine 6B 0.003 parts by weight Sample H Phthaloeyanine blue 0.003 parts by weight The suspensions thus prepared were added to the dye solution employed for Sample D in Example l well mixed and coated on an art paper sheet previously subjected to electroconductive treatment as in Example 1 to obtain a dried coating thickness of 10 microns. After I 1 drying, the coated paper was placed in a thermostatic box at 50C for 16 hours to harden the resinous binder. The photosensitive layers thus prepared (Samples F, G and H) were developed with a liquid developer containing carbon black toner and then dipped for 30 seconds in bleaching bath of the following composition at 25C:

An ordinary electrophotographic process consisting of electrostatic charging, imagewise exposure and developing was repeated three times with exposures of a multi-color original image through blue, green and red filters, respectively. Development was carried out with a liquid developer containing a yellow pigment of the following formula:

(Formula H) CH3 CH3 l I CH O s o=o Cl (:1 o o (;%CE- O H v H O Methyl alcohol 300 ml. to obtain a yellow image, quinacridone magenta to obi ggz 388 tain a magenta image and phthalocyanine blue to obn-buty l acetate tain a cyan image. After development, the photosensipotass'um h-"droxlde 20 tive layers were coated with a transparent lacquer The sensitizing dyes were exclusively removed from Samples F, G and H to provide reproductions with a black image on a background of pale yellow, pink and blue, respectively.

The photosensitive layers were then washed with methyl alcohol, dried and coated with the acrylic lacquer of Example 1 for surface protection to provide reproductions easily classifiable by background color.

In Example 3 exposure was with a tungsten through a transparency (illuminance: 100 lux., 1 sec.).

EXAMPLE 4 Samples B, C and D of Example 1, Samples E of Example 2, and Samples F, G and H of Example 3 were each laminated with a plastic film provided with an adhesive material containing a peroxide. ln Samples B, C, D and E, exposure to light for 5 hours provided results similar to those shown before, while Samples F, G and H had an appearance similar to that explained in Example 3 after light exposure for about 2 hours.

The plastic film employed for laminating was polyethylene terephthalate provided with a layer of adhesive which was a terpolymer of ethyl acrylate, N-vinyl- 2-pyrrolidone and N-tert-butylacrylamide (ethyl acrylate/N-vinyl-2-pyrrolidone/N-tertiary-butylacrylamide 55/20/25 (wt. ratio) intrinsic viscosity in acetone: 0.85 1.0) containing a small amount (0.02 wt.% based on the terpolymer resin) of tertbutylhydroperoxide. Lamination was carried out by means of a heated roll.

EXAMPLE 5 Instead of the Sample D in Example 1, which was found to be unsuitable for multi-color reproduction because of its unbalanced spectral sensitivity under tungsten light, the combinations of dyes set out below was employed. The photosensitive layer prepared was reddish in fresh state, but the reproduction background changed to a neutral color after light exposure for 2 hours after coating with a lacquer containing peroxides.

ln this example, a dye solution of the following composition was added to 100 gr. of zinc oxide.'

Sample I 3-B-carboxyethyl-2(3,3-dicyanoallylidenehenzolhiazole mg. Rose bengal l0 mg. C.l. direct blue (Cl. 74180) 5 mg. Methanol l0 mg.

which contained polyisobutyl methacrylate as a nonvolatile component and butyl acetate as a solvent which contained benzoyl peroxide in an amount of 0.1 wt.% (based on the non-volatile component).

According to this invention, it is thus possible to obtain an electrophotographic photosensitive material free from the drawbacks resulting from uneven spectral sensitivity upon repeated exposures which is capable of showing a neutral residual color after development.

EXAMPLE 6 The photosensitive layer shown in Example 2 was laminated with a polypropylene film provided with an adhesive layer consisting of 80 parts by weight of polybutyl methacrylate, 20 parts by weight of an aliphatic polyester (Japan Reichhold; D-tite 307 MH), 0.005 parts by weight of dieumyl peroxide and 0.005 parts by weight of benzoyl peroxide. Lamination was accomplished by passing the photosensitive sheet and the film between rolls heated to C after the photosensitive sheet was developed with an isoparaffinic liquid developer containing carbon black toner and washed with an isoparaffinic solvent free of toner. The sheet was still wet with the solvent when lamination was conducted. 7

' After lamination, the photosensitive layer gradually changed color to show a final blue background.

What is claimed is: l. A process for toning an electrophotographic layer comprising the steps of forming a developed image on an electrographic layer comprising a photoconductive powdered material, a resinous binder, and at least two coloring materials selected from the group consisting ofsensitizing dyes and pigments and mixtures thereof at least one of said coloring materials being a sensitizing dye or sensitizing pigment, said two coloring materials having different fading rates and being further selected from at least two of the following groups: group (a) comprising coloring materials 2. A process as in claim 1 where said coloring materials are Selected from groups (a) and (c).

. 3. A process as in claim 1 where said coloring materials are selected from groups (b) and (c).

4. A process as in claim 1 where said coloring materialsare selected from groups (a), (b), and (c).

, 5. A process as in claim 1 where said group (a) coloring materials are selected from the group consisting of cyanine' and merocyanine dyes.

6. A process as in claim 1 where said group (b) coloring materials are selected from the group consisting of azo dyes, anthraquinone dyes, phthalocyanine dyes, phthalocyanine pigments, q uinacridone pigments, azo pigments and cadmium sulfide.

7. A process as in claim 1 wheresaid group (c) coloring materials are selected from the group consisting of triphenylmethane dyes, xanthene dyes, and sulfonephthalein dyes.

8. A process as in claim' 1 where the coloring materials of group (e) have agreater spectral sensitizing ef-' fect than the group (a) and (b) coloring materials.

9. A process as in claim 1 hwerein said bleaching is effected by applying a transparent lacquer containing a peroxide, the amount of said peroxide being within the range of 0.000l 0.1 gram/meter? I 10. A process as in claim 9 where said range extends from 0.0001 0.01 gram/meter? 11. A process as in claim 1 wherein said bleaching is effected by laminating a transparent plastic'film on said 'electrophotographie layer using an adhesive which contains a peroxide, the amount of said peroxide being within the range of 0.000l O.l-gram/meter 12. A process as in claim 11 wherein said adhesive is selected from the group consisting of a polyvinylacetate,- a polyethylacrylate, a vinylacetate-ethylacrylate copolymer, a vinylacetate-ethylene copolymer, a plyethylhexymethacrylate,Ian aliphatic polyester, a

xylene-formaldehyde resin, natural rubber, resin and a hydrogenated resin.

13. A process as in claim 11 where the amount ofsaid peroxide is within the range of 0.0001 0.1 gram/- meter 14. A process as in claim 13 where said range extends from 0.0001 0.01 gram/meter? 15. A process as in claim 1 where said resinous binder is selected from a group consisting of a silicone resin, an alkyd resin, a polyvinylchloride, a polyvinylacetate, a vinylchloridevinylacetate copolymer, a polystyrene, a polyalkylmethacrylate, a polyalkylacrylate, a styrene-butadiene copolymer, an epoxy resin, and an epoxy ester resin.

16. A process as in claim 1 where said two coloring materials comprise at least two sensitizing dyes.

17. A process as. in claim 1 where said two coloring materials comprise at least one sensitizing dye and at least one pigment.

18. A process as in claim 2 where said coloring material of group (c) is selected from said sensitizing dyes to neutralize the color of said electrophotographic layer, the spectral sensitivity of said electrophotographic layer being enhanced by at least-one coloring material of group (a).

19. A process as in claim 1 where said coloring mate rials are selected from groups (a) and (b).

20. A process as in claiml9 where said coloring ma terial of group (a) is selected from blue-green sensitizing dyes and said coloring material of group (b) is sev lected from red-sensitizing dyes.

21. A process as in claim'l where said electrophotographic layer tends to turn yellow, said coloring material of group (b) being a phthalocyanine dye and those of (a) and (b) being selected to neutralize the color of said electrophotographic layer. 

1. A PROCESS FOR TONING AN ELECTROPHOTOGRAPHIC LAYER COMPRISING THE STEPS OF FORMING A DEVELOPED IMAGE ON AN ELECTROGRAPHIC LAYER COMPRISING A PHOTOCONDUCTIVE POWDERED MATERIAL, A RESINOUS BINDER, AND AT LEAST TWO COLORING MATERIALS SELECTED FROM THE GROUP CONSISTING OF SENSITIZING DYES AND PIGMENTS AND MIXTURES THEREOF AT LEAST ONE OF SAID COLORING MATERIALS BEING A SENSITIZING DYE OR SENSITIZING PIGMENT, SAID TWO COLORING MATERIALS HAVING DIFFERENT FACING RATES AND BEING FURTHER SELECTED FROM AT LEAST TWO OF THE FOLLOWING GROUPS: GROUP (A) COMPRISING COLORING MATERIALS HAVING AN ABSORPTION RATE VARIATION GREATER THAN 15%; GROUP (B) COMPRISING COLORING MATERIALS HAVING AN ABSORPTION RATE VARIATION LESS THAN 3%; AND GROUP (C) COMPRISING COLORING MATERIALS HAVING AN ABSORPTION RATE VARIATION FROM 3 TO 15%; AND SELECTIVELY BLEACHING AT LEAST ONE OF SAID COLORING MATERIALS SO THAT AT LEAST ONE OF SAID COLORING MATERIALS REMAINS IN SAID ELECTROPHOTOGRAPHIC LAYER TO THEREBY TONE SAID LAYER.
 2. A process as in claim 1 where said coloring materials are selected From groups (a) and (c).
 3. A process as in claim 1 where said coloring materials are selected from groups (b) and (c).
 4. A process as in claim 1 where said coloring materials are selected from groups (a), (b), and (c).
 5. A process as in claim 1 where said group (a) coloring materials are selected from the group consisting of cyanine and merocyanine dyes.
 6. A process as in claim 1 where said group (b) coloring materials are selected from the group consisting of azo dyes, anthraquinone dyes, phthalocyanine dyes, phthalocyanine pigments, quinacridone pigments, azo pigments and cadmium sulfide.
 7. A process as in claim 1 where said group (c) coloring materials are selected from the group consisting of triphenylmethane dyes, xanthene dyes, and sulfonephthalein dyes.
 8. A process as in claim 1 where the coloring materials of group (c) have a greater spectral sensitizing effect than the group (a) and (b) coloring materials.
 9. A process as in claim 1 hwerein said bleaching is effected by applying a transparent lacquer containing a peroxide, the amount of said peroxide being within the range of 0.0001 - 0.1 gram/meter2.
 10. A process as in claim 9 where said range extends from 0.0001 - 0.01 gram/meter2.
 11. A process as in claim 1 wherein said bleaching is effected by laminating a transparent plastic film on said electrophotographic layer using an adhesive which contains a peroxide, the amount of said peroxide being within the range of 0.0001 - 0.1 gram/meter2.
 12. A process as in claim 11 wherein said adhesive is selected from the group consisting of a polyvinylacetate, a polyethylacrylate, a vinylacetate-ethylacrylate copolymer, a vinylacetate-ethylene copolymer, a polyethylhexymethacrylate, an aliphatic polyester, a xylene-formaldehyde resin, natural rubber, resin and a hydrogenated resin.
 13. A process as in claim 11 where the amount of said peroxide is within the range of 0.0001 - 0.1 gram/meter2.
 14. A process as in claim 13 where said range extends from 0.0001 - 0.01 gram/meter2.
 15. A process as in claim 1 where said resinous binder is selected from a group consisting of a silicone resin, an alkyd resin, a polyvinylchloride, a polyvinylacetate, a vinylchloridevinylacetate copolymer, a polystyrene, a polyalkylmethacrylate, a polyalkylacrylate, a styrene-butadiene copolymer, an epoxy resin, and an epoxy ester resin.
 16. A process as in claim 1 where said two coloring materials comprise at least two sensitizing dyes.
 17. A process as in claim 1 where said two coloring materials comprise at least one sensitizing dye and at least one pigment.
 18. A process as in claim 2 where said coloring material of group (c) is selected from said sensitizing dyes to neutralize the color of said electrophotographic layer, the spectral sensitivity of said electrophotographic layer being enhanced by at least one coloring material of group (a).
 19. A process as in claim 1 where said coloring materials are selected from groups (a) and (b).
 20. A process as in claim 19 where said coloring material of group (a) is selected from blue-green sensitizing dyes and said coloring material of group (b) is selected from red-sensitizing dyes.
 21. A process as in claim 1 where said electrophotographic layer tends to turn yellow, said coloring material of group (b) being a phthalocyanine dye and those of (a) and (b) being selected to neutralize the color of said electrophotographic layer. 